Well if you want to create multiple live accounts, you have to press the Middle Button on the Controller (that turns it on) and then click on create new account. Make sure that you are not signed in. If you want them to be allowed on Xbox Live, you have to pay for it, or make them a silver account, and they will give you a free month of Xbox Live.

To buy MS points, you can do that on your 360. When you are on the Marketplace, you can go to add Microsoft Points. You can purchase 500 Points at the least, and like 6000 points (or something like that) at the most.